Hi All, Regarding the sherry colored Topaz from Utah. I was told by
the operator of the local Rock Shop that Yes they will fade if not
radiated.

Cannot say from experience but I suspect the Utah Topaz is a lot like
the Mexican I experimented with some 25 years ago,still cooling for
the next 100-200 years.On exposure to irradiation,these sherry Topaz
are activated to Cesium.The half life is centuries. Don’t confuse this
with the ligher color grades of Imperial Topaz from Ouro
Preto,Brazil.They too would appear intially sherry color. These take
irradiation and go to dark Red Orange.Again I would like to speak only
from experience,but no one has done enough of them or kept records to
determine the stability.By reputation and my personal
experience,some,likely most will fade on exposure to sunlight.The
idea of stablizing with ultraviolet light does not seem logical.It
would serve for fade testing.That is of course where the idea of
stablizing might come in.If it stands up to it,it won’t fade in
future.When testing for light sensitivity,take care to expose the
stones to ultraviolet light,not the heat of the sun.All irradiated
material,and many natural materials will fade when heated.Overzelous
testers in say a Florida USA enviornment,may leave a fine gemstone out
on the patio for a week or two weeks.In direct sunlight,the stone can
be cooked to temperatures in excess of 500F,think about a stone in the
sun,gets so hot you burn your finger to touch.So therefore many a
tester has decreed that a certain stone will fade in the sun.It is not
the light,it is the heat.These tests are not fair examples of normal
wear and tear. Before this post get construed that all dark color Ouro
Preto Imperial Topaz fades,I want to state that natural dark Ouro
Preto Imperial Topaz is stable to sunlight and reasonable
heat.Certainly 500F.What you might experience is some of the very dark
Orange,can go Pink in the sunlight.This phenomenon is like when you
have a natural Peach Morganite,and leave it in the sun for a while,it
goes to stable Pink Morganite. Mark Liccini http://www.LICCIN.com